The present invention relates to a golf ball characterized by good rebound resilience and good workability with which it is produced.
In an attempt to impart good rebound resilience to golf balls, various improvements have been made on the formulation of polybutadiene as a base material for golf balls.
Among such improvements is a new rubber compound for solid balls which was disclosed in Japanese Patent Laid-open No. Sho 62-89750, for example. This rubber compound is composed of a polybutadiene (as the base material) having a Mooney viscosity of 70 to 100, which is synthesized by using a nickel or cobalt catalyst, and another polybutadiene having a Mooney viscosity of 30 to 90, which is synthesized by using a lanthanum-based catalyst, or another polybutadiene having a Mooney viscosity of 20 to 50, which is synthesized by using a nickel or cobalt catalyst.
However, the rubber compound mentioned above still needs further improvements on extrusion workability and rebound resilience.
Also, there is disclosed in Japanese Patent Laid-open No. Hei 2-268778 a golf ball which is molded from a blend of a polybutadiene having a Mooney viscosity less than 50, which is synthesized by using a group VIII element catalyst, and another polybutadiene having a Mooney viscosity less than 50, which is synthesized by using a lanthanide catalyst. This golf ball, however, is poor in rebound resilience.
Moreover, there is disclosed in Japanese Patent Laid-open No. Hei 11-70187 a multi-piece solid golf ball having an intermediate layer formed from a polybutadiene having a low Mooney viscosity. There is disclosed in Japanese Patent Laid-open No. Hei 11-319148 a solid golf ball formed from a rubber compound composed of a polybutadiene having a Mooney viscosity of 50 to 69, which is synthesized by using a nickel or cobalt catalyst, and another polybutadiene having a Mooney viscosity of 20 to 90, which is synthesized by using a lanthanoid-based catalyst. There is disclosed in Japanese Patent Laid-open No. Hei 11-164912 a solid golf ball formed from a rubber compound which contains no more than 2.0% of 1,2-vinyl bond and has an Mw/Mn ratio no larger than 3.5 (which is a ratio of weight-average molecular weight to number-average molecular weight). There is disclosed in Japanese Patent Laid-open No. Sho 63-275356 a golf ball which is formed from a rubber compound containing a polybutadiene having a high Mooney viscosity. There is disclosed in Japanese Patent Laid-open No. Hei 3-151985 a golf ball which is formed from a rubber compound composed of two kinds of polybutadiene, one having a high number-average molecular weight and the other having a low number-average molecular weight. However, the disclosed rubber compounds are all poor in extrusion workability and they merely give golf balls poor in rebound resilience.
Also, there is disclosed in Japanese Patent Laid-open No. Hei 6-190083 a blend composed of a polybutadiene having a high Mooney viscosity and an isoprene rubber having a high Mooney viscosity. This blend, however, is not necessarily satisfactory in workability and rebound resilience. There is disclosed in Japanese Patent Laid-open No. Sho 60-94434 a polybutadiene compounded with zinc acrylate, zinc methacrylate, and isoprene rubber in a specific ratio. This compound, however, is not satisfactory in rebound resilience because the polybutadiene has a low Mooney viscosity. A similar rubber compound is disclosed in Japanese Patent Laid-open No. Hei 4-109971; however, it is still poor in rebound resilience because the polybutadiene has a low Mooney viscosity. Incidentally, Japanese Patent Laid-open No. Hei 2-297384 discloses a fact that rebound resilience is improved by addition of an organosulfur compound or a metal containing organosulfur compound.